Potassium-modified ZSM-5 zeolite for catalytic coupling methanol with butene to propylene

Abstract

K-doped ZSM-5 zeolites (K-ZSM-5) were prepared by equal volume impregnation, ion exchange and in situ isomerization methods. Equal volume impregnation can effectively increase the specific surface area of zeolite, regulate the proper balance of weak and strong acid centers, and introduce more K into the ZSM-5 zeolite skeleton. K–O interaction produces a suitable pore structure, which provides more active centers and reduces carbon deposition. K-ZSM-5 prepared by equal volume impregnation showed good catalytic activity in methanol coupled with butene to propylene when the amount of potassium was 1.45 wt %. Under the temperature of 550 °C, pressure of 0.4 MPa, methanol/butene (molar ratio) of 1/1 and WHSV of 1800 mL/(g_cat·h), Operating at temperature of 550 °C, pressure of 0.4 MPa, molar ratio of methanol to butene of 1:1, and WHSV of 1800 mL/(g_cat·h), the butene conversion was 74.9 %, accompanied by a propylene selectivity of 42.2 % and STY of 20.8 mol/(g_cat·h). Density Functional Theory (DFT) calculations showed that doping K to ZSM-5 can make –OH of methanolate of higher electronegativity, further strengthen the interaction between oxygen and the catalyst surface, stabilize the adsorption of butene on the catalyst, and facilitate coupled methanol with butene to generate light olefins.